Abstract：
Numerous mechanisms can drive speciation, including isolation by adaptation, distance, and environment. These forces can promote genetic and phenotypic differentiation of local populations, the formation of phylogeographic lineages, and ultimately, completed speciation. However, conceptually similar mechanisms may also result in stabilizing rather than diversifying selection, leading to lineage integration and the long-term persistence of population structure within genetically cohesive species. Processes that drive the formation and maintenance of geographic genetic diversity while facilitating high rates of migration and limiting phenotypic differentiation may thereby result in population genetic structure that is not accompanied by reproductive isolation. We suggest that this framework can be applied more broadly to address the classic dilemma of \"structure\" versus \"species\" when evaluating phylogeographic diversity, unifying population genetics, species delimitation, and the underlying study of speciation. We demonstrate one such instance in the Seepage Salamander (Desmognathus aeneus) from the southeastern United States. Recent studies estimated up to 6.3% mitochondrial divergence and four phylogenomic lineages with broad admixture across geographic hybrid zones, which could potentially represent distinct species supported by our species-delimitation analyses. However, while limited dispersal promotes substantial isolation by distance, microhabitat specificity appears to yield stabilizing selection on a single, uniform, ecologically mediated phenotype. As a result, climatic cycles promote recurrent contact between lineages and repeated instances of high migration through time. Subsequent hybridization is apparently not counteracted by adaptive differentiation limiting introgression, leaving a single unified species with deeply divergent phylogeographic lineages that nonetheless do not appear to represent incipient species.
摘要：
许多机制可以驱动物种形成，包括通过适应隔离，距离,和环境。这些力量可以促进当地人群的遗传和表型分化，系统地理谱系的形成，最终,完成的物种形成。然而,概念上相似的机制也可能导致稳定而不是多样化的选择，导致遗传凝聚力物种内的谱系整合和种群结构的长期持久性。驱动地理遗传多样性的形成和维持，同时促进高迁移率和限制表型分化的过程可能因此导致不伴有生殖隔离的种群遗传结构。我们建议在评估系统地理多样性时，可以更广泛地应用此框架来解决“结构”与“物种”的经典困境。统一群体遗传学，物种划界,以及物种形成的基础研究。我们在美国东南部的SeepageSalamander（Desmognathusaeneus）中展示了一个这样的例子。最近的研究估计高达6.3％的线粒体差异和四个系统基因组谱系，在地理杂种区广泛混合，这可能代表我们的物种划界分析支持的不同物种。然而,虽然有限的分散促进了距离的实质性隔离，微生境特异性似乎在单个上产生稳定的选择，制服,生态介导的表型。因此,气候周期促进了谱系之间的反复接触，并随着时间的推移反复出现高迁移。随后的杂交显然没有被适应性分化限制性基因渗入所抵消，留下一个统一的物种，其系统地理谱系差异很大，但似乎并不代表初期物种。
